Long-term Sequestration Research Articles

Silicon in Plants: Alleviation of Metal(loid) Toxicity and Consequential Perspectives for Phytoremediation.

For the majority of higher plants, silicon (Si) is considered a beneficial element because of the various favorable effects of Si accumulation in plants that have been revealed, including the alleviation of metal(loid) toxicity. The accumulation of non-degradable metal(loid)s in the environment strongly increased in the last decades by intensified industrial and agricultural production with negative consequences for the environment and human health. Phytoremediation, i.e., the use of plants to extract and remove elemental pollutants from contaminated soils, has been commonly used for the restoration of metal(loid)-contaminated sites. In our viewpoint article, we briefly summarize the current knowledge of Si-mediated alleviation of metal(loid) toxicity in plants and the potential role of Si in the phytoremediation of soils contaminated with metal(loid)s. In this context, a special focus is on metal(loid) accumulation in (soil) phytoliths, i.e., relatively stable silica structures formed in plants. The accumulation of metal(loid)s in phytoliths might offer a promising pathway for the long-term sequestration of metal(loid)s in soils. As specific phytoliths might also represent an important carbon sink in soils, phytoliths might be a silver bullet in the mitigation of global change. Thus, the time is now to combine Si/phytolith and phytoremediation research. This will help us to merge the positive effects of Si accumulation in plants with the advantages of phytoremediation, which represents an economically feasible and environmentally friendly way to restore metal(loid)-contaminated sites.

Environmentally Sustainable Large-Scale CO2 Sequestration through Hydrates in Offshore Basins: Ab Initio Comprehensive Analysis of Subsea Parameters and Economic Perspective

Immediate measures are required to tackle global warming and climate change that may require the storage of enormous quantities of anthropogenic CO2 in geological and oceanic reservoirs. In terrestrial storage sites, CO2 is buoyant due to the subsurface temperature profile. Therefore, if the reservoir is not adequately sealed, stored CO2 can escape from geological formations. Alternatively, oceanic sequestration has immense potential to facilitate long-term sequestration of CO2 beneath the seafloor, thereby assisting the wider scientific and industrial community to make the world carbon neutral. There is a far-reaching scope for discussion in this aspect that will open up new avenues for future developments in this area. This article discusses the long-term viability, environmental sustainability and economic potential of CO2 sequestration in the form of hydrates into oceanic and subsea sediments. Analysis shows that at above 2800 m depth, CO2 is denser than seawater, which offers an additional gravitation barrier for CO2 to escape. This article offers an in-depth analysis of CO2 sequestration conditions, along with challenges and outlook with relevance to hydrate-based CO2 sequestration in oceanic conditions. Moreover, the crucial role of negative buoyancy and hydrate-forming zones (NBZ/HFZs) and analysis of depth criterion in oceanic conditions have been highlighted. The review also envisages that sequestration in NBZ region offers stable storage for years even in geological perturbation and earthquakes; however the depth of HFZ and NBZ regions depends on sedimentary type, storage conditions, temperature and pressure.

Salvage decision-making based on carbon following an eastern spruce budworm outbreak

Forest disturbances, such as an eastern spruce budworm (Choristoneura fumiferana) outbreak, impact the strength and persistence of forest carbon sinks. Salvage harvests are a typical management response to widespread tree mortality, but the decision to salvage mortality has large implications for the fate of carbon stocks (including forest carbon and harvested wood products) in the near and long terms. In this study, we created decision-support models for salvage harvesting based on carbon after an eastern spruce budworm outbreak. We used lasso regression to determine which stand characteristics (e.g., basal area) are the best predictors of carbon 40 years after an outbreak in both salvage and no salvage scenarios. We modeled carbon at year 40 for different treatment scenarios and discount rates. Treatment scenarios represent residual stand conditions that may be present when an outbreak occurs. Economic discount rates were applied to 40-year carbon values to account for near and long-term carbon storage aspects. We found that the volume and size of eastern spruce budworm host species are significant predictors of salvage preference based on carbon. We found overall that salvaging less volume is recommended to avoid major swings in carbon budgets and that discounting carbon values to apply weight to near or long-term sequestration greatly affects whether salvaging is preferred. Lasso models are constructed for the northeastern US, however, similar concepts may be applied beyond our study area and potentially for other insect outbreaks similar to spruce budworm, such as mountain pine beetle (Dendroctonus ponderosae) or hemlock woolly adelgid (Adelges tsugae). From a policy standpoint widespread salvaging could create a large carbon emissions deficit with the risk of not being fully replenished within a desired timeframe. Since salvaging is often financially driven, especially for private landowners, carbon market payments or incentives for not salvaging is a consideration for future policy.

Fate and cost effectiveness of soil carbon sequestered using supplementary nutrients applied to crop residues under field conditions

Changes in carbon (C) and nitrogen (N) associated with fine fraction (FF) soil organic matter (SOM) were determined to a depth of 1.80 m at a field site that was managed with supplementary nutrients (2007–2012) to sequester soil C from crop residues. Soil C and N stocks were monitored for a further 3 years (to 2015) with supplementary nutrients maintained, and then for 5 years after they were ceased (2015–2020). The increase in FF-C established in the first phase of nutrient addition (9.6 Mg C ha−1) was maintained during the ongoing 3 year period of nutrient addition (9.8 Mg C ha−1) but declined to 3.0 Mg C ha−1 during the subsequent 5 years when nutrient addition ceased. The decline in FF-C stocks was attributed to both less formation of FF-C without the supplementary nutrients applied, and to nutrient mining as insufficient N was being applied to both treatments to fully satisfy the N removed in crops. The addition of supplementary nutrients to the residue influenced crop yield in some years, and seed protein in most years, but the responses were crop and season dependant and there was no overall difference in the amount of C in crop biomass returned to the soil. An economic analysis using long-term fertiliser and grain prices suggested that the strategy to sequester more C in FF-SOM through nutrient addition to residue was essentially cost neutral. Better tailoring of nutrient inputs to achieve the required stoichiometric ratios in SOM, and an assumed payment for the sequestered C (AU$40 Mg−1 CO2 equivalent) provided a reliable economic benefit during the period of nutrient addition. However the economic benefit was lost when nutrient addition ceased, and would reduce if fertiliser prices increased or the C price declined. Our results confirm that addition of supplementary nutrients to C-rich crop residues is an effective means to sequester soil C that can persist for several years even after nutrient addition ceases. However, ongoing nutrient inputs in excess of crop removal are required to ensure long-term sequestration of the C from crop residue.

Guest Editorial: How To Leverage E&P Expertise for the New Energy Economy

_ The term “new energy economy” broadly refers to the transition to a low-carbon future for sustaining human development while reducing CO2 emissions. Such a shift is considered to be the third energy transition of the modern era, after the shift from biomass to coal as the primary source of energy in the early 1900s, followed by oil overtaking coal’s dominant position in the 1960s–1970s. This trend towards decarbonization (i.e., diversification from carbon-intensive fossil fuels to sustainable greener energy feedstocks and carriers) is motivated by the understanding that emissions need to be reduced to moderate the potential impacts of global temperature rise on future climatic changes. Strategies common to proposed decarbonization pathways include - Improving energy efficiency (i.e., slower increase in energy demand compared to GDP/population increase). - Increasing energy supply from renewable sources (i.e., wind, solar, geothermal, nuclear) coupled with hydrogen underground storage (HUS) as a way of storing surplus electrical energy. - Switching to low-carbon energy carriers (i.e., hydrogen) for end-use applications in transportation, buildings, and industry. - Removing carbon emissions, via carbon capture, utilization, and storage (CCUS), from fossil-fuel-fired power plants and hard-to-abate industrial sources. The key takeaway for readers is how the two subsurface-oriented decarbonization strategies—CCUS and HUS—are relevant for application/adaptation of expertise from the exploration and production (E&P) sector of the oil and gas industry. Their rise will be built upon decades of experience with CO2-EOR, gas injection, produced-water disposal, and underground natural gas storage (NGS). Carbon Capture, Utilization and Storage (CCUS) As shown in Fig. 1, CCUS involves capturing CO2 from a fossil-fuel-fired power plant or industrial facility and processing it to a practically pure form, transporting it to a nearby geologic storage site using pipelines, and injecting it into saline aquifers for long-term sequestration or depleted oil/gas fields for enhanced oil recovery (EOR) and associated storage. Research and field demonstration projects over the past few decades have demonstrated that CCUS is a viable technology for curtailing atmospheric CO2 emissions buildup. Some of the key elements of CCUS projects and their overlap with corresponding E&P expertise are summarized below.

Qualitative and Quantitative Changes in Soil Organic Compounds in Central European Oak Forests with Different Annual Average Precipitation

The various climate scenarios consistently predict warming and drying of forests in Hungary. Soils play a significant role in the long-term sequestration of atmospheric CO2, while in other cases they can also become net carbon emitters. Therefore, it is important to know what can be expected regarding future changes in the carbon storage capacity of soils in forests. We used precipitation gradient studies to solve this problem, using a type of “space–time” substitution. In this research, we primarily examined the quality parameters of soil organic matter (SOM) to investigate how climate change transforms the ratio of the main SOM compound groups in soils. For our studies, we applied elemental and 13C and 15N isotopic ratio analysis, NMR analysis, FT-IR spectra analysis, thermogravimetric and differential thermal analyses to measure SOM chemistry in samples from different oak forests with contrasting mean annual precipitation from Central Europe. Our results showed that soil organic carbon (SOC) was lower in soils of humid forests due to the enhanced decomposition processes and the leaching of Ca, which stabilizes SOM; however, in particular, the amount of easily degradable SOM compounds (e.g., thermolabile SOM, O-alkyl carbon, carboxylic and carbonyl carbon) decreased. In dry forest soils, the amount of recalcitrant SOM (e.g., thermostable SOM, alkyl carbon, aromatic and phenolic carbon and organo–mineral complexes stabilized by Ca increased, but the amount of easily degradable SOM increased further. The main conclusion of our study is that SOC can increase in forests that become drier, compensating somewhat for the decrease in forest plant biomass.

Intensification of the East Asian winter monsoon resulted in greater preservation of terrestrial organic carbon on the inner shelf of the East China Sea since the last 1400 years

The marine shelves of passive margins receive huge amount of terrestrial organic carbon (OC) exported from adjacent terrestrial ecosystems. Long-term sequestration of terrestrial OC into marine sediments plays an important role in the global carbon cycle on a range of timescales. However, our knowledge of factors affecting the fate of terrestrial OC in continental-marginal settings is incomplete, with ongoing debates regarding rates of degradation during transport and burial. In this paper, we employ analyses of total OC and its stable isotope (δ13C), terrestrial biomarkers and mineral surface area in sediment core 39-A obtained from mud-rich regions of the inner shelf of the East China Sea to investigate terrestrial OC burial history over the last 3000 years. Analysis of terrestrial lipid biomarker and terrestrial OC calculated based on a δ13C-binary mixing model shows increasing trends since ∼1400 yr BP, accompanied by a synchronous increase of terrestrial OC preservation rate. By compiling terrestrial OC records from mud-rich regions of the East China Sea inner shelf, we propose that the most reasonable explanation is the intensification of the East Asian Winter Monsoon. This resulted in a strengthening of coastal currents, which accelerated lateral transport speed (thereby shortening oxygen exposure time) of Changjiang (Yangtze River)-derived terrestrial OC towards the deposition site, resulting in greater terrestrial OC preservation. Moreover, we also found delayed responses of terrestrial OC burial to the East Asian Winter Monsoon in the middle and southern part of the Min-Zhe coastal mud region, implying that the transport of terrestrial OC towards this region took place on a centennial-time scale. Our study sheds new light on mechanisms controlling terrestrial OC transport and burial processes in a typical passive marginal sea.

Macroalgal habitats support a sustained flux of floating biomass but limited carbon export beyond a Greenland fjord

Despite growing attention on the contribution of macroalgae to carbon cycling and sequestration (blue carbon), more observational data is needed to constrain current estimates. In this study, we estimate the floating macroalgal carbon flux within and beyond a large sub-Arctic fjord system, Nuup Kangerlua, Greenland, which could potentially reach carbon sinks. Our study estimates 1) the fjord-scale area with macroalgal coverage and barrens caused by sea urchin grazing, 2) the floating macroalgal biomass in the fjord, and 3) the annual export flux of floating macroalgae out of the fjord system. ROV surveys documented that macroalgal habitats cover 32 % of the seafloor within the photic zone (0-30 m) with an average coverage of 39.6, 22, and 7.2 % in the depth intervals 0–10, 10–20, and 20-30 m, respectively. 15 % of the area suitable for macroalgae was denuded by sea urchin grazing. Floating macroalgae were common with an average biomass of 55 kg wet weight km−2. Densities and species composition varied seasonally with the highest levels after storms. The floating biomass was composed of intertidal macroalgal species (58 %) (Fucus vesiculosus, Fucus distichus, and Ascophyllum nodosum) and kelps (42 %) (Saccharina longicruris, S. latissima, and Alaria esculenta). We deployed surface GPS drifters to simulate floating macroalgal trajectories and velocity. Data indicated that 80 % of the floating biomass is retained in the fjord where its fate in relation to long-term sequestration is unknown. Export beyond the fjord was limited and indicated an annual floating macroalgal export beyond the fjord of only 6.92 t C yr−1, which is equal to ~0.02 % of the annual net primary production. Our findings suggest that floating macroalgae support a limited blue carbon potential beyond this fjord and that future research should focus on the fate of retained floating macroalgae and subsurface export to resolve the connectivity between macroalgal habitats and long-term carbon sinks.

Geochemical assessment of inorganic fluids from carbon capture, utilization and sequestration project in Saudi Arabia

Saudi Aramco has designed and implemented a geochemical monitoring and surveillance program for the first and largest Carbon Capture, Utilization and Sequestration project in the Middle East. The objective of this program is to quantify geochemical changes in reservoir fluids during water-flooding and CO2 injection to evaluate geochemical reactions, mixing processes during water alternating-gas (WAG) cycles, arrival times of injected fluids, sealing attributes for CO2 sequestration, and scaling tendencies. From 2012 to 2021, 280 time-lapse water samples from four CO2 producer wells, one gas-oil-separation plant, and nine shallow aquifer wells were analyzed and interpreted on the temporal variation of reactive elements (Ca, Mg, HCO3, SO4) and conservative parameters (Na, Cl). Except for one producer well, water-flooding did not alter the composition of produced water in observation wells. Almost three years after starting WAG, the arrival of injection fluid was detected in March 2018. Mixing of formation water with injection water resulted to be the dominant physical process. The abundance of heterogenous dolomite layers and elevated Ca/Mg and Ca/HCO3 ratios of produced water from one of the wells imply the partial interaction with specific reservoir horizons. Analogue geochemical trends point toward a hydraulically connected system for three of the producer wells, with sealing features for the fourth. The observed results are essential to calibrate CO2 reactive transport models for the prediction of a long-term sequestration of CO2. The lack of any communication between the reservoir formation and overlying groundwater zones assures in-situ confinement of CO2 as important conclusion of this study.

Fertilizer quality and labile soil organic matter fractions are vital for organic carbon sequestration in temperate arable soils within a long-term trial in Switzerland

Agricultural management of soils has led to severe losses of soil organic matter (SOM), accompanied by an increased release of CO2 into the atmosphere and a reduction of soil fertility. Especially under the aspect of global warming and the increasing demand for food, there is a need for sustainable management options increasing soil organic carbon (SOC) storage in agricultural soils, but knowledge gaps exist regarding C persistence in, and its transfer between functional SOC pools, within different farming systems. Here we report on impacts of different farming systems on the temporal dynamics of SOM fractions within the DOK long-term trial (Switzerland), from 1982 to 2017. A purely minerally (CONMIN), a minerally and organically (CONFYM), and a purely organically fertilized farming system (BIODYN) were compared with an unfertilized control (NOFERT). We separated archived soils from the Haplic Luvisol (0–20 cm depth) into particulate (POM) and mineral-associated OM (MAOM) fractions, via physical fractionation, and analyzed the chemical composition of selected fractions via solid-state 13C CPMAS-NMR spectroscopy. We demonstrate that under none of the analyzed farming systems, additional SOC was sequestered in the clay-sized MAOM fraction (<6.3 µm) over a period of 36 years. In all fertilized systems, the amount of SOC in this pool did not change, but strongly decreased in NOFERT (-27%). Bulk SOC increased in BIODYN (+13%) and CONFYM (+5%), but decreased in CONMIN (-8%) and NOFERT (-20%). As no additional SOC accumulated in the clay-sized MAOM fraction, this implies that bulk SOC increases were solely stored within labile POM fractions. NMR spectra showed comparable POM chemical compositions between different systems. Differences in fertilizer quality (BIODYN = composted farmyard manure vs CONFYM = stacked farmyard manure + mineral fertilizer) and the omission of pesticides resulted in better conditions for POM stabilization and consequently significantly higher C contents of occluded POM (oPOM) within aggregates, in BIODYN. However, this labile fraction is at high risk of being lost within a few days, as illustrated by the strong annual oPOM-C content fluctuations depending on the timing of soil sampling after harvest. The highest post-harvest oPOM-C losses in BIODYN indicate the higher dynamics compared to CONFYM. It is anticipated that only sustainable fertilization methods with continuous application of solely organic fertilizers in the long-run can maintain SOC in the labile POM fractions at elevated levels, thereby ensuring soil fertility. It also illustrates the need for prevention of major losses by careful management of the labile POM fractions, as this OM could associate with fine mineral particles at a later stage and thus contribute to OC sequestration in the stable SOC pool. Overall, the potential of arable soils to accumulate stable OC for long-term sequestration is questioned.

Coupled dynamics of aqueous biogeochemistry in contrasting floodplain environments: Implications for Critical Zone carbon sequestration along redox gradients

This study contributes to our evolving understanding of how coupled biogeochemical dynamics of Fe and Mn along the redox gradients affect C cycling and sequestration at Critical Zones. A 12-month monitoring of the in-situ soil pore-water biogeochemistry and redox gradients across the floodplain at the White Clay Creek Watershed in the Christina River Basin - Critical Zone Observatory was investigated. Topographically, eastern floodplain was narrow with a steep hillslope connected to the agricultural field while western floodplain was flat and wide. Soil profile consisted of post-colonial oxic deposits, pre-colonial anoxic buried wetland soils underlain by suboxic valley-bottom gravel. Contrasting soil pore-water chemistry including DOM quality, DOC, Fe and Mn, δ18O and δD profiles, and redox potentials were observed between the eastern and western floodplains due to seasonal fluctuations, divergent topographic and hydrologic settings. We observed diverse types of C pools across the floodplain from short (labile) to long term (recalcitrant) C forms: microbial origin DOM at eastern versus terrestrial or plant-derived DOM at western buried wetland soil pore-waters. Gravel was linked to the soluble microbial byproduct-like fractions indicating bioavailable DOM and microbial activity. Gravel beds may act as a natural filter (or C sink) of terrestrial DOM via adsorption and precipitation with Mn- and Fe (hydr)oxides, stimulating the long-term sequestration of sedimentary OC while retaining the microbially-derived DOM in the pore-water. In contrast, reductive dissolution of Mn- and Fe (hydr)oxides may result in re-mobilization of aromatic DOM and increase of DOC flux (C source) to the stream. Future studies are needed to improve our understanding of how in-situ redox gradients and/or microbial activity transform OC-mineral complexes and the coupled C dynamics at Critical Zones.

Soil carbon sequestration by root exudates.

Root exudates are well-known 'labile' sources of soil carbon that can prime microbial activity. Recent investigations suggest that the stability of labile carbon inputs in soil mostly depends upon the physical, chemical, and biological properties of the surroundings. Here, we propose that, in some ecosystems, such as forests and grasslands, root exudates can function as a source of soil organic carbon (SOC) that can be stabilized through various mechanisms leading to long-term sequestration. Increasing soil carbon sequestration is important for capturing atmospheric CO2 and combating climate change issues. Thus, there is an urgent need to preserve existing ecosystems and to adopt strategies such as afforestation, reforestation, and establishment of artificial grasslands to foster carbon sequestration through higher root exudate inputs in the soil.

A generalizable framework for spatially explicit exploration of soil organic carbon sequestration on global marginal land

Land-based CO2 removal demands changes in management or new suitable areas to sustainably grow additional biomass without reducing food supply or damaging natural ecosystems. The soil organic carbon (SOC) sequestration pathway is thought to transfer atmospheric CO2 into a land unit, through plants, plant residues and other organic solids stored as part of the soil organic matter. No previous study explored SOC sequestration potentials on global marginal land. Here we integrated, into a generalizable modelling framework, the mapping of a set of biophysical (climatic and edaphic) and land conservation constraints to (i) identify suitable matches (i.e. biophysically possible combinations) of target areas with plant species, and (ii) to quantify contributions of pairing to long-term SOC sequestration (2020–2100). The proposed framework represents a refinement to previous mapping exercises, which seldom consider biophysical constraints, soil erosion, plant species tolerances to pedoclimatic conditions, and world protected areas. The approach was tested on marginal lands featuring SOC-deficient stocks (≤ 50 Mg SOC ha−1 to 30 cm depth) at 30 arc-sec resolution, consolidated into world regions × global ecological zones based on geo-localised products. The framework was shown to enable better-informed decision-making on interventions at large geographical scales, revealing biophysically realistic options, while management should be determined locally.

Human skin-resident host T cells can persist long term after allogeneic stem cell transplantation and maintain recirculation potential.

Tissue-resident memory T cells (TRM) have recently emerged as crucial cellular players for host defense in a wide variety of tissues and barrier sites. Insights into the maintenance and regulatory checkpoints of human TRM cells remain scarce, especially due to the difficulties associated with tracking T cells through time and space in humans. We therefore sought to identify and characterize skin-resident T cells in humans defined by their long-term in situ lodgment. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) preceded by myeloablative chemotherapy unmasked long-term sequestration of host T cell subsets in human skin despite complete donor T cell chimerism in the blood. Single-cell chimerism analysis paired with single-cell transcriptional profiling comprehensively characterized these bona fide long-term skin-resident T cells and revealed differential tissue maintenance for distinct T cell subsets, specific TRM cell markers such as galectin-3, but also tissue exit potential with retention of the transcriptomic TRM cell identity. Analysis of 26 allo-HSCT patients revealed profound interindividual variation in the tissue maintenance of host skin T cells. The long-term persistence of host skin T cells in a subset of these patients did not correlate with the development of chronic GvHD. Our data exemplify the power of exploiting a clinical situation as a proof of concept for the existence of bona fide human skin TRM cells and reveal long-term persistence of host T cells in a peripheral tissue but not in the circulation or bone marrow in a subset of allo-HSCT patients.

Phytolith-Occluded Carbon Sequestration Potential of Oil Palm Plantation in Tamil Nadu.

Oil palm (Elaeis guineensis) has proven to be a phytolith-occluded carbon (PhytOC)-rich species that plays a vital role in acting as a carbon sink for reducing atmospheric carbon dioxide (CO2) concentration. The present research estimated the silicon, phytolith, and PhytOC contents in four (OP4), eight (OP8), and fifteen (OP15)-year-old oil palm plantations. Qualitative analysis using a scanning electron microscope (SEM) revealed the presence of abundant globular echinate phytoliths with varied diameter (8.484–10.18 μm) in fronds, empty fruit bunches, and roots. Furthermore, a wide band (400–490 cm–1) underlined a higher relative abundance of Si–OH groups in empty fruit bunches, fronds, and roots, which emphasized the amorphous nature of silica. Quantitative analysis revealed that the phytolith (phytolith/dry biomass), PhytOC (PhytOC/phytolith), and PhytOC (PhytOC/dry biomass) contents in all oil palms differed significantly (p < 0.05) and increased with age. The PhytOC stock showed significant variation, with the trend of OP15 > OP8 > OP4. The belowground biomass of OP4 (16.43 g kg–1) and OP8 (17.13 g kg–1) had a maximum PhytOC concentration compared to the aboveground biomass, and the belowground proportion varied from 20.62 to 20.65%. The study demonstrated a positive correlation between the phytolith and PhytOC contents of oil palm; thereby, oil palm should be cultivated for enhanced long-term sequestration as a phytolith accumulator.

Source and Accumulation of Soil Carbon along Catena Toposequences over 12,000 Years in Three Semi-Natural Miscanthus sinensis Grasslands in Japan

Miscanthus-dominated semi-natural grasslands in Japan appear to store considerable amounts of soil C. To estimate the long-term effect of Miscanthus vegetation on the accumulation of soil carbon by soil biota degradation in its native range, we measured total soil C from the surface to a 1.2 m depth along a catena toposequence in three annually burned grasslands in Japan: Kawatabi, Soni, and Aso. Soil C stock was estimated using a radiocarbon age and depth model, resulting in a net soil C accumulation rate in the soil. C4-plant contribution to soil C accumulation was further estimated by δ13C of soil C. The range of total soil C varied among the sites (i.e., Kawatabi: 379–638 Mg, Soni: 249–484, and Aso: 372–408 Mg C ha−1). Catena position was a significant factor at Kawatabi and Soni, where the toe slope soil C accumulation exceeded that of the summit. The soil C accumulation rate of the whole horizon in the grasslands, derived C mainly from C4 plant species, was 0.05 ± 0.02 (Average ± SE), 0.04 ± 0.00, and 0.24 ± 0.04 Mg C ha−1 yr−1 in Kawatabi, Soni, and Aso, respectively. Potential exists for long-term sequestration of C under M. sinensis, but the difference in the C accumulation rate can be influenced by the catena position and the amount of vegetation.

Economic potential for carbon sequestration by short rotation eucalypts using biochar in Florida, USA

Above- and below-ground carbon sequestration by Eucalyptus depends on management options, which in Florida include short rotation woody crops (SRWC) and windbreaks (WB). Applying growth and economic models to E. grandis and E. grandis x E. urophylla cultivars grown as SRWCs and to E. grandis cultivars in a related WB, with and without soil amendments including biochar (BC), we developed preliminary estimates of their carbon sequestration potentials. The cultivars may sequester over 10 Mg of C/ha/year as SRWCs. Under the assumed management costs and market conditions, SRWC management with BC will be more profitable than operational culture if BC application costs are ≤$450/Mg. In WBs, E. grandis cultivars may sequester up to 34 Mg of C/ha in three years, with additional sequestration by amending soil with BC. Using BC, e. g., derived from eucalypts, as a soil amendment is both a long-term sequestration strategy and an opportunity to increase plantation and crop productivity.

Greenhouse Gas Inventory Model for Biochar Additions to Soil.

Stabilizing the global climate within safe bounds will require greenhouse gas (GHG) emissions to reach net zero within a few decades. Achieving this is expected to require removal of CO2 from the atmosphere to offset some hard-to-eliminate emissions. There is, therefore, a clear need for GHG accounting protocols that quantify the mitigation impact of CO2 removal practices, such as biochar sequestration, that have the potential to be deployed at scale. Here, we have developed a GHG accounting methodology for biochar application to mineral soils using simple parameterizations and readily accessible activity data that can be applied at a range of scales including farm, supply chain, national, or global. The method is grounded in a comprehensive analysis of current empirical data, making it a robust method that can be used for many applications including national inventories and voluntary and compliance carbon markets, among others. We show that the carbon content of biochar varies with feedstock and production conditions from as low as 7% (gasification of biosolids) to 79% (pyrolysis of wood at above 600 °C). Of this initial carbon, 63–82% will remain unmineralized in soil after 100 years at the global mean annual cropland-temperature of 14.9 °C. With this method, researchers and managers can address the long-term sequestration of C through biochar that is blended with soils through assessments such as GHG inventories and life cycle analyses.

Managing and treating per- and polyfluoroalkyl substances (PFAS) in membrane concentrates.

Per- and polyfluoroalkyl substances (PFAS), which are present in many waters, have detrimental impacts on human health and the environment. Reverse osmosis (RO) and nanofiltration (NF) have shown excellent PFAS separation performance in water treatment; however, these membrane systems do not destroy PFAS but produce concentrated residual streams that need to be managed. Complete destruction of PFAS in RO and NF concentrate streams is ideal, but long-term sequestration strategies are also employed. Because no single technology is adequate for all situations, a range of processes are reviewed here that hold promise as components of treatment schemes for PFAS-laden membrane system concentrates. Attention is also given to relevant concentration processes because it is beneficial to reduce concentrate volume prior to PFAS destruction or sequestration. Given the costs and challenges of managing PFAS in membrane concentrates, it is critical to evaluate both established and emerging technologies in selecting processes for immediate use and continued research.

Aggregate-related changes in living microbial biomass and microbial necromass associated with different fertilization patterns of greenhouse vegetable soils

Knowledge on soil aggregation and microbial-driven soil C dynamics at the aggregate scale is beneficial for long-term sequestration of C in greenhouse vegetable production (GVP) systems. Here, we used an eight-year fertilization experiment to compare the effects of organic vs. chemical fertilization on soil aggregate stability, as well as living microbial biomass, microbial necromass, and soil C dynamics at the aggregate scale. Relative to chemical fertilization treatment, organic amendments (e.g., manure and/or straw) could improve soil physical quality (as indicated by the value of mean weight diameter), increase microbial biomass and residues, as well as enhance the contributions of microbes to soil organic C (SOC) accumulation within large macroaggregates, small macroaggregates, microaggregates, and silt/clay fractions. Microbial biomass and residues were unevenly distributed among aggregates under different fertilization patterns, i.e., organic amendments made microbial biomass and fungal residues enriched from in silt/clay fractions to in macroaggregates. The low proportions of microbial residue C in SOC in microaggregates demonstrated that the microhabitat of microaggregates limits microbial necromass contributions to SOC accumulation. The changes of microbial biomass were closely related to extractable organic C (EOC), while the variations of fungal and bacterial residues were intimately associated with its corresponding microbes (i.e., fungal and bacterial PLFAs) and enzymes. Moreover, microbial associated ratios (e.g., fungal/bacterial PLFAs) were largely influenced by aggregates and strongly associated with soil chemical associated ratios (e.g., EOC/EON). Our findings provide useful insights on soil microbial-driven C dynamics at the aggregate scale in GVP systems under different fertilization patterns in China.